1. Field of the Invention
The invention relates to a coating-forming liquid composition capable of forming a coating for bonding copper to a photosensitive resin and to a coating-forming method using the composition.
2. Description of the Related Art
Physical polishing such as buffing and chemical polishing such as soft etching are generally used to pre-treat a copper surface, on which a resist will be formed, in a printed circuit board-manufacturing process including forming a plating resist or an etching resist on the cupper surface using a photosensitive resin (photoresist) and patterning the resist. These polishing processes aim not only to activate the copper surface but also to roughen the copper surface so that the adhesion to the photosensitive resin can be improved by an anchoring effect.
Unfortunately, there have been increasing cases where physical polishing or chemical polishing is difficult due to a reduction in the thickness of an insulating layer-carrying substrate itself or a reduction in the thickness of a copper layer itself on which a resist will be formed (a reduction in thickness due to the use of electroless plating or the like), so that there have been increasing cases where rust removal with dilute sulfuric acid is alternatively used to activate the surface of copper. In recent years, a problem has also occurred with the adhesion between the surface of copper and a patterned resist in the activation process with dilute sulfuric acid, due to a reduction in the line width or size of the pattern to be formed, so that a reduction in productivity is now taking place.
More specifically, a photosensitive resin layer formed on the surface of copper is exposed to light and then developed with a developer such as an aqueous sodium carbonate solution, and the developed pattern is used as a plating resist or an etching resist in the next process, but if the resist does not have reliable adhesion in the plating process or the etching process, the desired pattern shape cannot be obtained. In particular, an electroless-plated copper layer formed as a conductive layer on an insulating layer is thin and difficult to be polished. Therefore, it has been required to establish a technique capable of improving the adhesion between the surface of copper and a photosensitive resin without polishing.
Patent document 1 listed below proposes a copper surface treatment agent capable of improving the adhesion of a photosensitive resin even to a copper surface not capable of being polished physically or chemically, which comprises an aqueous solution containing a specific heterocyclic compound and having a pH of 4 or less. When the surface of copper is treated with this copper surface treatment agent, a coating containing the specific heterocyclic compound is formed on the surface of copper, and the surface of copper is bonded to the photosensitive resin with the coating interposed therebetween, so that reliable adhesion applicable to fine line patterns can be achieved. It should be noted that when the copper surface treatment agent disclosed in patent document 1 is used in a pretreatment before the formation of a plating resist, the exposed coating generally has to be removed using an acid liquid or the like after the formation of the plating resist and before electroplating.